The portrait lens

Although almost any lens can be used to take portraits of people, some
are more effective and easier to use than others. Wide angle lenses are
not a good choice, but they require you to work very close to your
subject in order to fill the frame with just head and shoulders. The
close viewpoint results in perspective distortion and makes the subject
feel uncomfortable besides.

So called normal lenses allow for better perspective than wide angles,
but they still call for too close a viewpoint. On the other hand, very
long focal length lenses magnify the image too much and have to be used
so far from the subject that indoor portraiture becomes impractical.

The best size portrait lens for any camera
is one with a focal length of 1.5 to 2 times normal. In the 35mm camera
filed this covers focal lengths from about 80mm to 105mm. Such a lens
allows you to position your camera at a comfortable distance, providing
good perspective while still filling the frame with a close up view.

If wire sharp images of the proper size are
satisfactory for your purpose, then an ordinary lens of about double the
normal focal length will serve you well. However, if in addition you
desire portraits that possess an alluring softness – a glowing quality
that subdues wrinkles and other defects while enhancing the subject –
you will need a special purpose optic known as a portrait lens.

Times ago, even the best lenses obtainable
were burdened with so many aberrations (defects) that really sharp
images were impossible to achieve. This was a drawback for many kinds of
photography, but not for portraits.

Over the years, as aberrations were tamed
and image quality improved, lenses lost their characteristic flattering
softness of earlier times. But since it was a defect known as spherical
aberration that had caused the glowing fuzziness admired by so many
portrait photographers, lens deliberately retained this one. The result
was lenses that offered a whole range of soft focus effects, depending
upon how far they were stopped down. (Spherical aberration is caused by
the light rays which enter around the edges of a lens, coming to a focus
at a different point from those entering through the center. Therefore,
a portrait lens is softest at its widest aperture, but gets sharper
gradually as it is stopped down. At f/8 or so and beyond the resolution
is equal to that or any ordinary lens.)

Early portrait lenses were designed for use
on large studio cameras only. Now these special purpose optics are also
available for all DSLR cameras. Today the choice of f-stops is not the
only means of controlling the degree of softness. Movable internal lens
components, filters that block out parts of the light beam, or metal
inserts that look like sink strainers also help to regulate the amount
of diffusion.

You should understand that soft focus is not
the same as out of focus. A sharp lens thrown out of focus renders
everything mushy and unsatisfactory but a carefully focused portrait
lens delivers an image in which every part of the subject is both in and
out of focus at the same time. The effect is charming and romantic.

Keep in mind the fact that a portrait lens,
while it is ideal for its intended purpose, needn’t be confined to
pictures of people. Landscapes and many other subjects can also benefit
from the velvety softness. The possibilities inherent in this versatile
optics are limited only by a photographer’s imagination.

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